(1) Field of the Invention
The present invention relates to a reamer shoe for use in drilled well bores as are typically utilised in oil and gas production.
(2) Description of Related Art
After boring a region of an oil or gas well it is normal to run tubing or “casing”, into the well bore to act as a lining. The casing is typically run into the well bore from the surface and the length of casing is often referred to as a “casing string”. The lining of the bore can then be strengthened by introducing cement between the external surface of the casing and the internal surface of the well bore.
It is common for the casing to meet obstructions as it is run through the well bore. These may be ledges which form in the well bore material during boring, formation washouts, or debris formed by unstable sections of the well bore wall collapsing. Such obstructions halt the progress of the casing procedure and increase the risk of the casing string jamming in the bore. To prevent or minimise the effect of these obstructions a reamer shoe is conventionally mounted on the lower end of the casing string. The reamer shoe typically has a plurality of reaming members around the circumference of the shoe body, which remove any irregularities or obstructions from the wall of the bore and thereby facilitate the subsequent passage of the casing string and aid cementing.
In conventional reamer shoes, the reaming members extend parallel to the length of the shoe. Whilst this arrangement allows the reaming members to come into contact with the entire circumference of the bore well on rotation of the shoe, complete circumferential coverage of the bore well is not achieved when the shoe is reciprocated.
An attempt has been made to mitigate this problem in International Patent Application PCT/GB99/00093 in the name Downhole Products plc. This Application discloses a reamer shoe with reaming members which extend longitudinally and helically around, as opposed to longitudinally and parallel to, the shoe body. More specifically the reaming members extend helically around the body of the shoe in an opposite direction to the intended direction of rotation.
While this arrangement of reaming members gives full 360° coverage during both reciprocating and rotation, the efficiency of said members is very much dependent on the speed and also the direction of rotation. It will be appreciated that the quality of reaming action will be compromised at relatively high rotational speeds. In addition, the reaming action of the shoe is designed to be most efficient when the reaming members extend in the opposite direction to rotation; therefore if the shoe was rotated in the same direction as the reaming members extend, either intentionally or accidentally, the risk of the reaming members “biting” into the wall and hence becoming stuck in the bore would be increased. It would therefore be a distinct advantage to provide a reamer shoe which is equally effective on rotation and reciprocation, and which provides an efficient reaming action regardless of the speed and direction of rotation.
It is an object of the present invention to provide a reamer shoe for reaming a bore in preparation for receiving casing, wherein said reaming shoe is equally effective on rotation or reciprocation.
It is a further object of the present invention to provide a reamer shoe for reaming a bore in preparation for receiving casing, wherein said reaming shoe is efficient at cleaning a bore when rotated, regardless of the speed or direction of rotation.